FIGS. 1A, 1B, and 1C are three side elevation views and FIG. 1D is a work end view of a conventional twist drill 10. The three side elevation views of FIGS. 1A, 1B, and 1C show twist drill 10 in different angular orientations of and about its longitudinal axis 12 to clearly present certain structural features. Specifically, twist drill 10 has a body that includes an elongated shaft 14 extending between a tip 16 and a shank 18. Each of a pair of flutes 20 spirals along the length of shaft 14 and has a trailing edge 22 and a sharpened leading cutting edge 24. Two top relief portions 26 provide at a work end downwardly sloping surfaces that form a taper from tip 16 to the full diameter of shaft 14.
FIGS. 2A, 2B, and 2C show twist drill 10 in, respectively, a reference (substantially 0 degrees) angular orientation about longitudinal axis 12, a 90 degree angularly displaced orientation about longitudinal axis 12 relative to that of FIG. 2A, and the orientation of FIG. 2B with an outwardly directed tilt from the plane of the figure. FIG. 2D is an enlarged fragmentary view of the work end of twist drill 10 in the angular orientation shown in FIG. 2A. Increasing amounts of the lengths of trailing edge 22 and leading cutting edge 24 of shaft 14 contact the wall of a hole cut by twist drill 10 as it plunges into a work piece (not shown). The contact of shaft 14 against the hole wall creates friction between twist drill 10 and the work piece. This friction generates heat stored in twist drill 10 and necessitates energy to overcome drag slowing the rate of plunge of twist drill bit 10 into the work piece. Moreover, twist drill 10 is not configured to accommodate lateral cutting movement in a drilled hole to facilitate correction of axial misalignment of holes in two work pieces positioned to be joined by a fastener inserted in them.
What is needed, therefore, is a twist drill bit configured to reduce the amount of friction produced and thereby reduce the amounts of heat generated and energy consumed during cutting a hole into a work piece. Reducing energy consumption would be especially beneficial in the operation of a twist drill held in a cordless (i.e., battery operated) drill power head.